There doesn’t seem to be any way to get endangered toads brought to Mississippi from the Rocky Mountains to breed without letting them chill out, researchers have found. So, in their Deep South lab, boreal toads hibernate in a fridge and then a wine cooler.
Like many amphibians, the toads have been devastated by the chytrid fungus. Colorado and New Mexico list them as endangered, and Wyoming protects them. At Mississippi State University, researchers Natalie Calatayud and Cecilia Langhorne work with the endangered animals, through a partnership with the Memphis Zoo. They tried for two years to get the 4-inch-long toads to reproduce without hibernating, by using hormone injections.
Not one female laid eggs.
“It doesn’t matter how much hormone you give them,” Calatayud said — the eggs wouldn’t mature without maternal down time, even though scientists at the Cincinnati Zoo reported just that feat in 2009. The Cincinnati toads had been raised indoors and had never hibernated, and the Mississippi toads are aging, about 12 years old — reasons Calatayud said might be responsible.
So, to simulate hibernation conditions, Calatayud and Langhorne refrigerated the toads: four females for one month, four for three months and four for six months, then gave them hormone shots. Toads in all three groups laid eggs.
But the researchers don’t know whether the eggs were fertile. The male toads at their lab, after producing sperm for two years when there were no eggs, didn’t produce any sperm this year.
At Colorado’s Native Aquatic Species Restoration Facility, the hatchery has refrigerators with precise temperature controls that can be raised or lowered a couple of degrees at a time, superintendent Theo “Ted” Smith said.
But Calatayud and Langhorne use a standard refrigerator, set to 3 degrees Celsius — 37.4 Fahrenheit. Plastic boxes with moist earth on the bottom hold four toads each. They’re brought out every four or five days and sprayed with a mister as they hibernate. A week before waking time, they’re moved into the wine chiller, which is a bit warmer.
Boreal toads may be the most aquatic toads, spending most of their time as adults in the water, Calatayud said. That brings a water cooler into play, with water about 45 degrees Fahrenheit. “As soon as you bring them out of hibernation, they will automatically go into that cold water,” she said.
During hibernation, Calatayud said, “everything else shuts down. Everything the female has is invested into the growth and nutrition of these eggs.”
She has found that the toads will lay eggs after a much shorter hibernation than the five or six months normal in the Colorado Rocky Mountains.
The next research steps will include seeing whether a shorter hibernation lets females put on more weight and lay more eggs, she said. Another question is whether matings can be coordinated, so different groups — such as toads from specific areas — can be mated at different times.